You can also make use of %Library.Routine. As John pointed out a MAC routine will generate an INT routine, so if you have a situation where a MAC routine is saved but uncompiled you should check the INT code.

You can use the LastModifiedMethod(), here is an example

   set myRoutine =  ##class(%Routine).%OpenId("MyFavoriteRoutine.INT")

   write myRoutine.LastModifiedMethod()

If you are working a lot with routines, %Library.Routine has more functionality which you might find useful.